If you’re still in touch with who built the house, they may know if there’s a header, LVL, or whatever in the wall. Assuming they built it to plan, it’d be on the plan.
When I worked for a home builder we wouldn’t put a header in for no reason. That wall would have probably been 2x4 with some kind of beam over the opening but just 2x4 in the actual wall.
Edit to add my paint interpretation of how it may be framed

Probably a bottom plate, a top plate or 2, with 2x4 16" spacing. Some kind of header over the opening with a king and jack studs supporting it.